The present invention relates generally to radiocommunication systems and, more particularly, to techniques and structures for reducing the delay priority of comfort noise transmissions.
The cellular industry has made phenomenal strides in commercial operations both in the United States and the rest of the world. Growth in major metropolitan areas has far exceeded expectations and is rapidly outstripping system capacity. If this trend continues, the effects of this industry""s growth will soon reach even the smallest markets. Innovative solutions are required to meet these increasing capacity needs as well as to maintain high quality service and avoid rising prices.
In addition to the challenges posed by a need for greater system capacity, the designers of the remote units used in radio communication systems, e.g., mobile phones, have their own unique set of challenges. For example, a well known challenge in the industry is to extend the time between recharging batteries used to power these remote units, while at the same time continuing to provide additional functionality to satisfy subscriber demand. These competing desires have lead remote unit designers to search for creative ways in which to further reduce energy consumption in remote units.
As the radiocommunication industry matures, various subscriber usage patterns have been recognized. For example, it has been found that during a typical voice connection between two subscribers, the actual voice activity transmitted over the air interface accounts for less than 50% of the total connection time. Therefore, in an attempt to conserve power, remote units have been designed to actuate the transmission circuitry only during the voice-active portion of a call and render the transmission circuitry inoperative during periods of silence. This has been implemented, for example, using a detector for detecting voice activity and a discontinuous transmitter (DTX) that becomes inoperative when the voice activity detector (VAD) detects a pause in the user""s speech. As one skilled in the art will appreciate, this technique has been shown to reduce interference thereby leading to higher system capacity. The DTX technique also reduces power consumption of the remote units by turning off the transmitting circuitry for extended periods of time. Additional information regarding the use of a VAD in a discontinuous transmission system is described in commonly assigned, U.S. Pat. No. 5,881,373 to R. Elofsson et al., entitled xe2x80x9cMuting the Microphone in Radiocommunication Systems,xe2x80x9d the entirety of which is incorporated by reference herein.
While this technique has been shown to reduce interference and the power consumption of remote units, it poses a problem for reproduction of the voice signal at the receiving side. Specifically, since the transmitter is turned off during periods of silence, the background noise that would otherwise be transmitted over the air interface is not received by the other subscriber""s equipment. This, in turn, results in a reproduced voice that is discontinuous and includes audible artifacts, e.g., popping sounds.
One way to overcome this difficulty is to generate artificial background noise for reproduction at the receiving side when no voice signal is transmitted. This artificial background noise is commonly referred to as xe2x80x9ccomfort noisexe2x80x9d. Comfort noise can be generated by adaptive functions that monitor the background noise picked up by the microphone of a remote unit. When a pause in speech is detected, the comfort noise functions generate comfort noise information that is transmitted over the air interface instead of speech information. This information takes relatively little time to transmit, thereby allowing the transmitter to be turned off during most of each period of silence. At the receiving end, the comfort noise information is used to generate background noise so that the listener is not troubled by the discontinuity in transmission.
Such a comfort noise generation technique is currently available in GSM. Therein, a comfort noise evaluation algorithm is used in a remote unit""s speech encoder to create parameters that include information on the level and spectrum of the background noise. The evaluated comfort noise parameters are then encoded into a Silence Descriptor (SID) frame for transmission to the receiver. The SID frame is transmitted at the end of a speech burst, i.e., before the transmitter is switched off. As such, the SID frame also serves to initiate the comfort noise generation on the receiver side. If, after transmission of the first SID frame, the period of silence continues, SID update frames are transmitted by the remote unit. A SID update frame performs several functions. It indicates not only that the period of speech inactivity continues, but also that the cellular connection is still present. Moreover, the SID update frame serves to update the background noise detected at the remote unit.
The interval at which these SID update frames are transmitted depends on the type of speech coder employed. For example, for Full Rate (FR) and Enhanced Full Rate (EFR) speech coders in GSM, the rate at which SID frames are transmitted is FN MOD 104=52, where FN is the Frame Number. This corresponds to SID frames being transmitted approximately every 480 ms. For a Half Rate speech coder, the rate at which SID frames are transmitted is doubled, i.e. every 240 ms. Moreover, for the newly developed Adaptive Multi-Rate (AMR) speech coder, the SID transmit rate is predicted to be up to four times higher than for the FR or EFR coders, i.e. every 120 ms.
While speech has been and will continue to be an important part of mobile communications, usage of mobile communication equipment for transmission of data rather than speech has become increasingly popular by consumers over the past decade. The possibility to send and receive electronic mail and to use a web browser to obtain world-wide-web access is frequently discussed as services that will be more and more used in wireless communication systems.
There are fundamental differences between requirements for data communication and e.g., speech communication. For example, delay requirements are higher for speech, which is a real time service, and the error requirements are higher for data communication, while the delay constraints are lower. The use of packet data protocols, which are more suitable for transmission of data than circuit-switched protocols, starts to find its way into cellular communication systems. Packet service integration in both GSM cellular systems as well as DAMPS cellular systems is presently being standardized. As a result, cellular components (e.g., base transceiver stations, base station controllers, etc.) are being adapted to handle packet data services.
Therefore, when introducing packet data services into, for example, a GSM cellular system, designers need to consider the delay requirements of the information transmitted. For example, it is well established that speech is the most delay sensitive traffic and should be put into the highest priority class. Other services, which are more delay tolerant, such as packet data transmissions, can be put into a lower priority class. However, the conventional DTX technique within GSM is not conducive to such prioritization. For example, as set forth above, the conventional DTX technique in GSM specifies specific intervals at which SID update frames are transmitted. Under the conventional DTX scheme, these SID update frames, which are not as delay-sensitive as actual speech frames, are processed by the base transceiver station and base station controller at the same level of priority as speech frames. This is evident from the fact that the conventional DTX scheme correlates speech calls using the same FN counter irrespective of the speech activity. As such, the gain of statistical multiplexing (i.e., the ability to integrate calls based on the statistics of the speech source), which is common to the DTX scheme, is reduced thereby leading to higher bandwidth demands or longer speech delays.
There exists a need for a system and method that prioritizes information transmitted in a radiocommunication system so as to allow for better utilization of transmission resources.
The present invention seeks overcome the above deficiencies in the art by providing a system and method for reducing the delay of speech processing in a discontinuous transmission system. According to exemplary embodiments of the present invention, a base transceiver station assigns priority indicators to information received therein. When the information is speech or a first SID frame, a high priority indicator is assigned. When the information is a SID update frame, a low priority indicator is assigned. The information is transferred from the base transceiver station to a base station controller in an order determined by the priority indicators. As such, the delay in transferring and processing speech information is reduced.